Sodium Hypochlorite

Sodium Hypochlorite (liquid chlorine) is approximately 12% free available chlorine. Sodium hypochlorite must be stored in a covered tank and a room that is ventilated to the exterior. Liquid bleach is an acute health hazard and classified as a corrosive liquid.  It is relatively reactive with acidic chemicals and organics.

Liquid chlorine has some advantages, the most important being safer handling.  In a 12 percent solution, liquid chlorine is stronger than the 5 percent solution typical in household bleach and, as a liquid, it’s also relatively easy to monitor and introduce into pool water.  Liquid chlorine is injected into the main pool plumbing and is disseminated into the pool.  It’s easy to gauge and control.  Liquid chlorine costs approximately $1.35 per gallon. Its pH is 13.0.

Liquid chlorine also has its disadvantages.  Because of its short shelf life, liquid chlorine quickly loses its potency and effectiveness.  At the manufacturing facility, the liquid is mixed to a 14 to 16 percent solution, but typically deteriorates to about a 12 percent solution by the time it reaches the supplier and to a 10 percent solution at poolside.  Sodium hypochlorite is susceptible to the heat and sun and can drop to as low as a 5 percent solution in one month.  Shelf-life is typically between 30 and 50 days.  When the tanks are refilled, most are not cleaned out, and the new chlorine is diluted when added to the old chlorine.  As a result, potentially twice as much chlorine will be required to achieve the desired effect.  Therefore, storing liquid chlorine can quickly become a poor investment.

The maximum allowable quantity of sodium hypochlorite is 500 gallons when stored in an un-sprinklered area.  When stored in an area with an approved sprinkler system and approved storage containers, max allowable quantity increases by 100% for each (up to 2,000 gallons). Control areas for sodium hypo that do not exceed quantities listed shall have a 1-hour rated fire barrier separating the room from the rest of the building.

Where the quantity of liquid chlorine stored exceeds the MAQ, the control area must meet Protection Level 4 requirements per NFPA 1 and NFPA 400 and occupancy classification of H-4. This includes either a 2-or 4-hour fire rated separation depending on adjacent occupancies, 175ft travel distance for egress, and other requirements.

Secondary containment is required when using sodium hypochlorite. Secondary containment can either be achieved with a double-wall tank, a tank with secondary containment, or a dike wall.

As bleach tanks are not pressure-rated, nor do they need to be, it is not necessary for the tank that is specified to have an ASTM listing.

It is CH preference to use sodium hypochlorite on outdoor facilities (based upon availability and water testing).  If there is an indoor pool at the same site which is on calcium hypochlorite, specify calcium hypochlorite for the outdoor pool to stay consistent.  With medium pressure UV, sodium hypochlorite can now be used on indoor pools.

Sodium hypochlorite must be stored in a covered tank and a room that is ventilated to the outside.

When considering which type of chlorine delivery system to use on a high bather load water park with low dilution, consideration may be given to a preference for liquid depending on availability and compatibility with other pools the owner operates.

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